1. Field
Aspects of the example implementations relate to a real-time three-dimensional radiation therapy apparatus and method for Intensity Modulated Radiation Therapy (IMRT). More particularly, the example implementations relate to a real-time three-dimensional radiation therapy apparatus and method that detects beam data such as radiation field shape, irradiation direction, intensity, dose, dose distribution, and the position and shape of a treatment target for each delivery of therapeutic radiation, and feeds these results back to the next irradiation in real time.
2. Related Art
Radiation therapy is carried out, in general, in accordance with the flowchart shown in FIG. 10. Patients who undergo radiation therapy are subjected to detailed imaging of a treatment target using diagnostic imaging equipment including a CT scanner prior to the actual course of radiation treatment, in order to identify the treatment targets (step S1). The physician develops, on the basis of the image data obtained by the imaging, a treatment plan for determining a set of irradiation conditions such as the radiation field shape, irradiation direction, intensity, dose, and dose distribution of the radiation (step S2). Prior to carrying out the radiation therapy, the developed treatment plan is simulated using X-ray simulators, or measured and evaluated using a phantom, to verify the accuracy and validity of the treatment plan (step S3). In particular, in the case of IMRT, this pretreatment verification is important because of the complex combination of irradiation conditions. The related art preparation from imaging with a CT scanner through the completion of verification takes about one to two weeks. Next, the patient progresses to the step of radiation therapy (step S4). The patient is fixed in the same body position as the body position used in the development of the treatment plan and exposed to radiation (steps S5 and S6). The number of treatment sessions varies depending on the state of the disease. For example, in the case of prostate cancer, each individual treatment session lasts for approximately 20 minutes and is continued once a day for from 36 times to 39 times (steps S7 and S8). Therefore, a full course of therapy requires approximately seven to eight weeks.
The therapy requires such a long period of time because, with related art radiation therapy apparatuses, it is not possible to intensively irradiate only the tumorous tissue with a dose of radiation sufficiently high to kill only the tumorous tissue in a single exposure without also harming surrounding healthy tissue. Conventional radiation therapy apparatuses have radiation beam resolutions only on the order of 1 cm, and are thus unable to irradiate only tumorous tissue with a high degree of accuracy, not only in the case of tumorous tissue 1 cm or smaller in size but also at the boundaries between tumorous tissue and healthy tissue in the case of tumors larger than 1 cm. Thus, a dose of radiation that is low enough to not harm healthy tissue but which is still effective against tumorous tissue has to be delivered separately many times over multiple sessions. This divided irradiation thus kills the tumorous tissue by abnormal division, while the healthy tissue can recover even if it suffers some radiation damage.
The present applicant has previously filed an application for patent for an X-ray therapy apparatus which can track the movement of a treatment target of a patient in real time, and provide X-ray therapy at high speed with a high degree of accuracy from every direction to match the three-dimensional shape of the treatment target using high-power, small-diameter or small-breadth X-ray beams, titled “X-RAY THERAPY EQUIPMENT” (Japanese Patent Application No. 2009-75008), which was patented on Dec. 11, 2009 as Japanese Patent No. 4418888 (JP-4418888-B), and for which a corresponding U.S. patent issues on Jan. 22, 2013 as U.S. Pat. No. 8,358,737. The X-ray therapy apparatus described in JP-4418888-B includes an X-ray generation source for outputting high-energy X-rays of 1 MV or more, moreover while continuously varying the beam diameter or breadth of the X-rays in a range of from 1 mm to 10 mm. This X-ray generation source has made it possible to carry out X-ray irradiation with a high degree of accuracy to match the three-dimensional shape of the treatment target. The X-ray therapy apparatus described in JP-4418888-B includes, as shown in FIG. 8, a therapeutic X-ray sensor 71 for moving in conjunction with the movement of a therapeutic X-ray generator 70 while remaining opposite the therapeutic X-ray generator 70. This therapeutic X-ray sensor 71 is a sensor for detecting X-ray beam data such as the radiation field, intensity, direction, dose, and dose distribution of the therapeutic X-rays passing through the treatment target. The data acquired by this sensor is processed in real time and fed back to the next irradiation, thereby providing high-accuracy therapy.
However, the information on the therapeutic X-rays is only data on the therapeutic X-rays after the X-rays have passed through the treatment target; the actual dose absorbed by the treatment target has to be estimated from the treatment plan data. In addition, accuracy suffers because the irradiation direction of the therapeutic X-ray is detected in one plane only. Furthermore, in the X-ray therapy apparatus described in JP-4418888-B, the radiation field is formed by an X-ray tube array consisting of a bundle of X-ray tubes for outputting small-diameter or small-breadth X-ray beams, and thus, in the case of irradiating a large area, the procedure for forming the radiation field can be complicated.
As described above, the conventional radiation therapy requires a long period of time to completion. Therefore, in order to reduce the total therapy time, it has been proposed that the verification process prior to actual radiation treatment be shortened.
Thus, for example, the invention described in JP-2010-508106-A (national stage entry of PCT/EP2007/061787; published as WO/2008/053026) discloses a verification method that eliminates the need for the conventional measurement and evaluation using a phantom. The delivery of radiation is carried out toward a two-dimensional transmission detector, and on the basis of the detection results and data such as a beam model parameter, a beam model, and a mechanical parameter set, the fluence is calculated in accordance with a fluence calculation algorithm. Next, using the calculated fluence, three-dimensional image data including information on the shape and density of a treatment target, and a dose algorithm, the three-dimensional dose distribution is acquired with respect to the treatment target.
However, the three-dimensional dose distribution acquired in accordance with the dose algorithm is a calculated dose distribution, which is problematic in terms of accuracy because the actual dose may differ considerably from the calculated dose. Furthermore, the disclosure of JP-2010-508106-A fails to make any reference to post-treatment verification of results.
In short, the conventional art described above has several shortcomings. That is, conventional X-ray equipment suffers from inadequate detection accuracy of the therapeutic X-rays, that is, the X-rays used for treatment. More specifically, detection of radiated X-ray beam characteristics, such as radiation field shape, irradiation direction, intensity, dose, and dose distribution, as well as the dose absorbed by the treatment target, is inadequate because only the X-rays passing through the treatment target are detected. In addition, it is not possible to reduce the duration of a course of therapy without degrading the accuracy of the radiation treatment. Furthermore, the treatment plan and verification thereof, as well as verification of the therapeutic outcome after therapy, require substantial time and effort.